1. Field of the Invention
The present invention relates to ceramic electronic components.
2. Description of the Related Art
Ceramic electronic components, typified by ceramic capacitors, are widely used in electronic devices, such as a cellular phone or a portable audio player. A ceramic electronic component generally includes a ceramic body; internal electrodes whose ends are exposed on the surface of the ceramic body; and external electrodes disposed to cover the surface regions of the ceramic body on which the internal electrodes are exposed. Examples of the external electrode include one obtained by applying and baking an electrically conductive paste to the ceramic body to form a sintered metal film and then plating the sintered metal film, as described in JP-A-2002-203737, and one formed only of a plating film, as described in JP-A-2004-327983.
However, because the electrically conductive paste used in forming the sintered metal film has high viscosity, the thickness of the resultant sintered metal film becomes large. For example, JP-A-2002-203737 states that the thickness of first and second electrode layers (sintered metal films) reaches approximately 50 μm to 90 μm.
Furthermore, if the external electrode is formed of a sintered metal film, the baking temperature at which the electrically conductive paste is baked reaches a high temperature. Therefore, a ceramic component in the ceramic body and a glass component in the electrically conductive paste may diffuse into each other to form a reaction layer at the interface between the ceramic body and the sintered metal film. In this case, a plating solution may enter the ceramic body through the site where the reaction layer is formed, which may cause a problem of a decrease in mechanical strength of the ceramic body and a problem of deterioration in reliability of moisture resistance thereof. In addition, the high baking temperature causes the precipitation of the glass component on the surface of the sintered metal film, i.e., glass floating, which presents another problem of difficulty in forming a plating film on the surface of the sintered metal film.
To cope with this, a method of making an external electrode only of a plating film is proposed as in JP-A-2004-327983. When an external electrode is made only of a plating film, the external electrode can be formed thinner than that formed by baking an electrically conductive paste, for example.
In addition, because the plating solution contains no glass component, no reaction layer is formed at the interface between the ceramic body and the plating film. Therefore, problems of a decrease in mechanical strength and deterioration in reliability of moisture resistance due to the formation of the reaction layer are less likely to occur. No glass floating occurs, so that the problem of difficulty in forming a plating film can be eliminated.
However, in order to form the external electrode only of a plating film, it is necessary to immerse the ceramic body directly into a plating solution. This presents a problem of entrance of the plating solution into the ceramic body through exposed portions of the internal electrodes. Thus, the resultant ceramic electronic component may decrease the moisture resistance.
Furthermore, when the external electrode is formed only of a plating film, the plating film is not only chemically but physically bound to the ceramic body, so that the adhesion between the plating film and the ceramic body will be poor. As a result, when the ceramic electronic component is in use, moisture or the like is likely to enter the ceramic body from between the plating film and the ceramic body. Also in this view, the resultant ceramic electronic component may decrease the moisture resistance.